1. Field of the Invention
The present invention relates to a method for producing a small solenoid, more particularly a superconducting solenoid made of compound oxide type superconducting material.
The small solenoid produced by the method according to the present invention is applicable in particular to a small and light-weight actuator, motor or generator, electromagnetic valve or the like.
The small solenoid according to the present invention may be integrated with active elements and/or passive elements on a common substrate consisting of semiconductor such as a single crystal of silicon.
2. Description of the Related Art
Superconducting coil or solenoid which is realized by metal type superconductor such as Ti-Nb alloy is already known and has been developed for a superconducting magnet or the like.
The critical temperature of the metal type superconductors, however, could not exceed 23.2.degree. K. of Nb.sub.3 Ge which which was the highest Tc for all studies for the past ten years and hence usage of liquidized helium (boiling point of 4.2.degree. K.) as cryogen is indispensable to realize superconductivity. Therefore, their actual application is limited to special industrial or scientific fields and still more it is difficult to reduce their size or diameter to less than several 10 mm at the present condition.
Possibility of existence of a new type of superconducting materials having much higher Tc was revealed by Bednorz and Muller who discovered a new oxide type superconductor in 1986 [Z. Phys. B64 (1986) 189]. This new oxide type superconducting material discovered by Bednorz and Muller is [La,Ba].sub.2 CuO.sub.4 which is called as the K.sub.2 NiF.sub.4 -type oxide having a crystal structure which is similar to a known perovskite type oxide. The K.sub.2 NiF.sub.4 -type oxides show such a high Tc as 30.degree. K. which is extremely higher than the known superconducting materials. It was also reported in the news parer that C. W. Chu et al. discovered in the United States of America another type of superconducting material having the critical temperature of about 90.degree. K. in Feb. 1987. This superconductor called as YBCO is a compound oxide of Ba-Y system represented by YBa.sub.2 Cu.sub.3 O.sub.7-.delta..
From the discovery of the abovementioned new type of compound oxide type superconductors, the realization of high-temperature superconductors which can realize the superconductivity in cheap and easily available liquidized nitrogen have arisen suddenly.
However, the abovementioned compound oxide is a ceramic material so that it is difficult or impossible to adopt directly the conventional technique which is used in the metal type superconductor for producing a solenoid or coil.
Therefore, an object of the present invention is to provide a method for producing a small superconducting solenoid or coil from the compound oxide which possesses a high critical temperature (Tc) at a reduced cost in an industrial scale.